1. Field of the Invention
The present invention relates to a data collecting apparatus for a loop-linked control system, and more specifically to an apparatus for collecting data stored in an internal memory of each system controller for a control system linked by a close coupled data transmission loop.
2. Description of the Prior Art
A prior-art plane control system will be described hereinbelow as an example of loop-linked control systems to which a data collecting apparatus of the present invention is applied.
In the plant control system shown in FIG. 1, a plurality of data transmit controllers 2, 3 and 4 are linked by a high speed large capacity data transmission loop 1 (e.g. optical fiber loop). Each of these data transmit controllers 2, 3 and 4 is provided with a common memory M.sub.1, M.sub.2 or M.sub.3, and connected to a plant controlling computer (CPU) 8 via an interface 5, to a process input/output (I/O) device 9 via an interface 6 and a plant controlling programmable controller (PC) 10 via an interface 7, respectively. Further, a sensor/actuator device 11 including various sensor, actuators (e.g. motors), indicators, terminals, etc. is connected to the process input/output (I/O) device 9. Further, although only a single plant controlling programmable controller 10 is shown in FIG. 1, in usual plural plant controlling programmable controllers 10 are connected to the close coupled data transmission loop 1 in order to distribute various functions of the system to the programmable controllers 10.
In the prior-art plant control system as shown in FIG. 1, process data outputted from the process I/O device 9 are momentarily transferred to the common memory M.sub.2 via the interface 6 and stored therein, and control data outputted from the CPU 8 and the plant PC 10 are momentarily transferred to the common memory M.sub.1 and M.sub.3, respectively via the interfaces 5 and 7 and stored therein. Further, various data once stored in these common memories M.sub.1, M.sub.2 and M.sub.3 are cyclically transferred between the three data transmit controllers 2, 3 and 4 via the data transmission loop 1. Accordingly, the most updated data of each of devices 8, 9 and 10 are stored in these common memories M.sub.1, M.sub.2 and M.sub.3, and further the devices 8, 9 and 10 can obtain an easy access to the updated data stored in the common memories M.sub.1, M.sub.2 and M.sub.3.
In the above prior-art control system, however, in case some accidents arise during plant control operation, there exists a need of collecting various data stored in the internal memory M.sub.i of the plant controlling programmable controller 10, for instance, in order to check the causes of the accidents. For doing this, the sensor/actuator device 11 is operated to execute a predetermined program so that data stored in the memory M.sub.i are first transferred to the common memory M.sub.3, the common memory M.sub.2 and then to an output terminal of the process I/O device 9, from which the data stored in the internal memory M.sub.i can be monitored through a recorder or on a display unit. However, since the data stored in the internal memory M.sub.i is not the common data cyclically transferred through the transmission loop 1, it has been necessary to use a special program maintenance tool or to modify input/output conversion addresses in the interface 6 or to alter programs of the plant controlling programmable controller 10, thus resulting in long time and much labor to collect data stored an internal memory of the plant controlling PC 10.